gardenia leaves turning yellow
I purchased/planted this gardening several weeks ago being very careful to sit the crown above the soil line. Leaves started turning yellow 2 weeks ago. At first I thought it was senescence of older leaves, but it is progressing up the stems. Is it just too much moisture from recent rain???
We think this is likely a combination of transplant shock and too much water.
The yellow leaves will brown, die and drop, but if all is well otherwise they will be quickly replaced by a flush of new growth.
Are they mulched? They'd like that, but no more than 2-3 inches, and it should be pulled back from touching the stem/crown/trunks of plants.
You should also consider testing your soil. Gardenias are acid-loving plants so they'd like a lower pH than most.
Here is our soil testing page: http://extension.umd.edu/hgic/soils/soil-testing
(Be sure to tell the lab you are growing Gardenias).
While we don't see any pests in your photos, be aware and monitor for scale insects and spider mites. These are less problematic outdoors than when we keep them as houseplants.